Most of the energy that reaches the Earth’s surface comes from the Sun (
Figure
below
). About 44% of solar radiation is in the visible light wavelengths, but the Sun also emits infrared, ultraviolet, and other wavelengths.

An image of the Sun taken by the SOHO spacecraft. The sensor is picking up only the 17.1 nm wavelength, in the ultraviolet wavelengths.

Ultraviolet

Of the solar energy that reaches the outer atmosphere,
ultraviolet (UV)
wavelengths have the greatest energy. Only about 7% of solar radiation is in the UV wavelengths. The three types are:

UVC: the highest energy ultraviolet, does not reach the planet’s surface at all.

UVB: the second highest energy, is also mostly stopped in the atmosphere.

UVA: the lowest energy, travels through the atmosphere to the ground.

Infrared

The remaining solar radiation is the longest wavelength,
infrared
. Most objects radiate infrared energy, which we feel as heat.

Some of the wavelengths of solar radiation traveling through the atmosphere may be lost because they are absorbed by various gases (
Figure
below
). Ozone completely removes UVC, most UVB, and some UVA from incoming sunlight. O
2
, CO
2
, and H
2
O also filter out some wavelengths.

Atmospheric gases filter some wavelengths of incoming solar energy. Yellow shows the energy that reaches the top of the atmosphere. Red shows the wavelengths that reach sea level. Ozone filters out the shortest wavelength UV and oxygen filters out most infrared.

Summary

Ultraviolet radiation has the highest energy; infrared the lowest.

Ultraviolet is divided into three categories based on wavelength: UVC, with the highest energy, UVB, and UVA, with the lowest energy.